So-called “three-dimensional printing” is a technique that has been developed and commercialised in various different ways. An early method involved focusing a laser onto a bath of photopolymerisable material to cause the material to polymerise where struck by the laser at and just below the surface of the bath. Layers of solid polymer can be built up to form a solid three-dimensional polymeric object.
Objects made from powdered materials can be made by a method that involves spreading a layer of powdered material over a build bed and depositing a liquid binder onto selected regions of the powder to produce bonded powder material at the selected regions. These steps are repeated a number of times to produce successive layers of selected regions of bonded powder material so as to form the desired object. This method has been described, for example in U.S. Pat. No. 5,387,380, US20051197431, US200610208388 and US200510252631. Three-dimensional printers that work on this principle are available commercially, for example from the company Z Corporation.
Three-dimensional printing with powdered materials has many advantages over conventional methods of manufacture. It allows bespoke objects to be manufactured very quickly and inexpensively. No support structures are needed since the excess powder which remains unbound acts as a support while the bonded layers are being built up to create the object. The object is designed using a computer aided design program and the steps of spreading a layer of powdered material and depositing a liquid binder onto it are controlled by the computer program. This means that objects of many different shapes can be built easily and quickly.
Some publications, including U.S. Pat. No. 5,387,380, have disclosed that “ceramic powder” can be used as the powdered material from which the object is made. Alumina, zirconia, zirconium silicate and silicon carbide are said to be representative ceramic materials. These materials are technically ceramic materials but are not a ceramic body comprising clay, as is used for conventional production of ceramic objects. In practice commercially available powdered materials for use in three-dimensional printing methods are usually limited to plaster and starch. It would, however, be desirable to be able to use the three-dimensional printing method to make ceramic objects.
Some research has been carried out into trying to make ceramic objects using the three-dimensional printing method with a conventional ceramic body (i.e. composition that is used to make ceramic objects) of the type that is typically used in a conventional process for manufacturing ceramics. Conventional ceramic bodies include clay, which exhibits plastic properties.
However, various problems have been encountered with using conventional ceramic bodies in a three-dimensional printing process. Compared to ceramic objects made by conventional ceramic manufacturing methods, the ceramic objects made with the same ceramic body by a three-dimensional printing method tend to have a higher fired shrinkage rate, a higher fired porosity, a lower strength and inferior surface detail. In addition, problems with the green strength of the object before firing can occur, giving rise to difficulties in removing the printed object from the build bed. Further problems have been encountered with the powder layers shifting during the printing process.
The present invention aims to provide an improved method for the production of ceramic objects by three-dimensional printing, and to solve some of the problems encountered to date with the ceramic bodies made by this process. In particular, the present invention aims to allow ceramic objects having improved properties to be made by a three-dimensional printing process, and preferably to allow ceramic objects to be made by a three-dimensional printing process that have comparably good properties to those made by conventional processes.